Much patent and technical art has developed around anhydride copolymers such as styrene-maleic anhydride copolymers. The polymers find many uses including molding resins, thermosettable resins when mixed with crosslinking agents such as glycols or diamines, aqueous thickeners and binders when converted to the salt form, etc.
Initial attempts to make similar copolymers of styrene and phenylmaleic anhydride produced relatively low molecular weight copolymers using conventional polymerization methods. To improve the physical properties, it was desirable to make high molecular weight copolymers. However, this proved to be difficult to accomplish.